Method and apparatus for performing access to cell

ABSTRACT

Provided are a method for a user equipment (UE) to perform access to a cell in a wireless communication, and an apparatus supporting the same. The method may include: receiving, from a first system, access control information for the first system; camping on the cell of a second system; mapping the access control information for the first system to access control information for the second system; and performing access to the cell of the second system, based on the mapped access control information for the second system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/257,459, filed on Jan. 25, 2019, which is a continuation pursuant to35 U.S.C. § 119(e) of International Application PCT/KR2018/005198, withan international filing date of May 4, 2018, which claims the benefit ofU.S. Provisional Patent Applications Nos. 62/502,591, filed on May 5,2017 and 62/501,824, filed on May 5, 2017, the contents of which arehereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method for a user equipment (UE) to performaccess to a cell and an apparatus supporting the same.

Related Art

In order to meet the demand for wireless data traffic, which has beenincreasing since the commercialization of a fourth-generation (4G)communication system, efforts are being made to develop an improvedfifth-generation (5G) communication system or pre-5G communicationsystem. For this reason, a 5G communication system or pre-5Gcommunication system is referred to as a beyond-4G-network communicationsystem or post-long-term evolution (LTE) system.

SUMMARY OF THE INVENTION

Meanwhile, new 5G NR access category will be applied for access control.As new 5G NR access category will be applied, 4G LTE access controlmechanisms cannot be applied for NR without any modification. Forexample, when the UE is connected to 5G-CN via E-UTRA, the NAS layers ofthe UE and the AMF that the UE is connected to will exchange NR NASsignaling messages. The serving eNB connected to 5G-CN may need tosupport enhanced LTE signaling messages or support only LTE messages.The latter may be preferred in order to minimize the modification impactof the eNB serving 5G-CN in that the RRC layers of the UE and the eNBcan exchange legacy LTE RRC messages. Here, the issue in the UE is thatthe NAS layer operation is based on NR protocol and the RRC layeroperation is based on LTE protocol. The RRC layer in 4G LTE may requireparameters such as establishment cause, call type, EAB indication, orACDC category from the NAS layer for access control. Therefore, the UEconnected to 5G-NAS via E-UTRA may require functionality for compatibleoperation to translate an access category into one or more LTE accesscontrol parameters. Hereinafter, a method for a UE to perform access toa cell and an apparatus supporting the same according to an embodimentof the present invention are described in detail.

One embodiment provides a method for performing, by a user equipment(UE), access to a cell in a wireless communication. The method mayinclude: receiving, from a first system, access control information forthe first system; camping on the cell of a second system; mapping theaccess control information for the first system to access controlinformation for the second system; and performing access to the cell ofthe second system, based on the mapped access control information forthe second system.

Another embodiment provides a user equipment (UE) performing access to acell in a wireless communication. The UE may include: a memory; atransceiver; and a processor, connected to the memory and thetransceiver, that: controls the transceiver to receive, from a firstsystem, access control information for the first system; camps on thecell of a second system; maps the access control information for thefirst system to access control information for the second system; andperforms access to the cell of the second system, based on the mappedaccess control information for the second system.

A UE can perform access control without signaling modification among theUE, the base station and the core network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem.

FIG. 3 shows a user plane of a radio interface protocol of an LTEsystem.

FIG. 4 shows 5G system architecture.

FIG. 5 shows functional split between NG-RAN and 5GC

FIG. 6 shows an example of access barring check.

FIG. 7 shows an example of access barring check for Application specificCongestion control for Data Communication (ACDC).

FIG. 8 is a block diagram illustrating access control mechanism for a UEconnected to 5G-CN via E-UTRA according to an embodiment of the presentinvention.

FIG. 9 is a block diagram illustrating access control mechanism for a UEconnected to 4G-CN via NR Radio Access (NR) according to an embodimentof the present invention.

FIG. 10 is a flow chart illustrating access control mechanism of a UEaccording to an embodiment of the present invention.

FIG. 11 is a block diagram illustrating a method for a UE to performaccess to a cell according to an embodiment of the present invention.

FIG. 12 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3rdgeneration partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced(LTE-A) is an evolution of the LTE. 5G communication system is anevolution of the LTE-A.

For clarity, the following description will focus on LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There are one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE_ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem. FIG. 3 shows a user plane of a radio interface protocol of anLTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L. The PHY layer provides a higherlayer with an information transfer service through a physical channel.The PHY layer is connected to a medium access control (MAC) layer, whichis a higher layer of the PHY layer, through a transport channel. Aphysical channel is mapped to the transport channel. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.Between different PHY layers, i.e., a PHY layer of a transmitter and aPHY layer of a receiver, data is transferred through the physicalchannel using radio resources. The physical channel is modulated usingan orthogonal frequency division multiplexing (OFDM) scheme, andutilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MICH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel. A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

Referring to FIG. 2, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARQ). TheRRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The PDCP layer (terminated in the eNB on the network side) may performthe user plane functions such as header compression, integrityprotection, and ciphering.

FIG. 4 shows 5G system architecture.

Referring to FIG. 4, a Next Generation Radio Access Network (NG-RAN)node may be either a gNB providing NR Radio Access (NR) user plane andcontrol plane protocol terminations towards the UE or an ng-eNBproviding Evolved Universal Terrestrial Radio Access (E-UTRA) user planeand control plane protocol terminations towards the UE. The gNBs andng-eNBs may be interconnected with each other by means of the Xninterface. The gNBs and ng-eNBs may be also connected by means of the NGinterfaces to the 5G Core Network (5GC), more specifically to the AMF(Access and Mobility Management Function) by means of the NG-C interfaceand to the UPF (User Plane Function) by means of the NG-U interface. TheNG-C may be control plane interface between NG-RAN and 5GC, and the NG-Umay be user plane interface between NG-RAN and 5GC.

FIG. 5 shows functional split between NG-RAN and 5GC

Referring to FIG. 5, the gNB and ng-eNB may host the followingfunctions:

-   -   Functions for Radio Resource Management: Radio Bearer Control,        Radio Admission Control, Connection Mobility Control, Dynamic        allocation of resources to UEs in both uplink and downlink        (scheduling);    -   IP header compression, encryption and integrity protection of        data;    -   Selection of an AMF at UE attachment when no routing to an AMF        can be determined from the information provided by the UE;    -   Routing of User Plane data towards UPF(s);    -   Routing of Control Plane information towards AMF;    -   Connection setup and release;    -   Scheduling and transmission of paging messages;    -   Scheduling and transmission of system broadcast information        (originated from the AMF or O&M);    -   Measurement and measurement reporting configuration for mobility        and scheduling;    -   Transport level packet marking in the uplink;    -   Session Management;    -   Support of Network Slicing;    -   QoS Flow management and mapping to data radio bearers;    -   Support of UEs in RRC_INACTIVE state;    -   Distribution function for NAS messages;    -   Radio access network sharing;    -   Dual Connectivity;    -   Tight interworking between NR and E-UTRA.

The Access and Mobility Management Function (AMF) may host the followingmain functions:

-   -   NAS signalling termination;    -   NAS signalling security;    -   AS Security control;    -   Inter CN node signalling for mobility between 3GPP access        networks;    -   Idle mode UE Reachability (including control and execution of        paging retransmission);    -   Registration Area management;    -   Support of intra-system and inter-system mobility;    -   Access Authentication:    -   Access Authorization including check of roaming rights;    -   Mobility management control (subscription and policies);    -   Support of Network Slicing;    -   SMF selection.

The User Plane Function (UPF) may host the following main functions:

-   -   Anchor point for Intra-/Inter-RAT mobility (when applicable);    -   External PDU session point of interconnect to Data Network;    -   Packet routing & forwarding;    -   Packet inspection and User plane part of Policy rule        enforcement;    -   Traffic usage reporting;    -   Uplink classifier to support routing traffic flows to a data        network;    -   Branching point to support multi-homed PDU session;    -   QoS handling for user plane, e.g. packet filtering, gating,        UL/DL rate enforcement;    -   Uplink Traffic verification (SDF to QoS flow mapping);    -   Downlink packet buffering and downlink data notification        triggering.

The Session Management function (SMF) may host the following mainfunctions:

-   -   Session Management;    -   UE IP address allocation and management;    -   Selection and control of UP function;    -   Configures traffic steering at UPF to route traffic to proper        destination;    -   Control part of policy enforcement and QoS;    -   Downlink Data Notification.

FIG. 6 shows an example of access barring check.

Referring to FIG. 6, in the overload or congest state of the network orthe base station, the base station may broadcast access class barring(ACB)-related information through system information. The systeminformation may be system information block (SIB) type 2.

The SIB type 1 may include ACB-related information like the followingtable.

TABLE 1 Field Description ac-BarringFactor When a random value generatedby the UE is smaller than a value of ac-BarringFactor, access isallowed. If not, the access is barred. ac-BarringForCSFB ACB for circuitswitch (CS) fallback. The CS fallback converts a VoLTE call to aprevious 3G call. ac-BarringForEmergency ACB for emergency serviceac-BarringForMO-Data ACB for mobile orienting dataac-BarringForMO-Signalling ACB for mobile orienting control signalac-BarringForSpecial AC ACB for specific access classes, that is, 11 to15. ac-BarringTime Represents time when the access is barred.ssac-BarringForMMTEL- ACB for each service for mobile orienting Video ofMMTEL video. ssac-BarringForMMTEL- ACB for each service for mobileorienting Voice of MMTEL voice.

Meanwhile, UE1 may determine an IMS service, for example, mobileorienting of a call by VoLTE and generates a service request message.Similarly, UE2 may determine mobile orienting of general data andgenerate the service request message.

Sequentially, the UE1 may generate an RRC connection request message.Similarly, the UE2 may generate the RRC connection request message.

Meanwhile, the UE1 may perform access barring check (that is, whetherthe ACB is applied). Similarly, the UE2 may perform access barring check(that is, whether the ACB is applied).

If the ACB is not applied, the UE1 and the UE2 may transmit the RRCconnection request message, respectively. However, when the ACB isapplied, both the UE1 and the UE2 may not transmit the RRC connectionrequest message, respectively.

The access barring check will be described in detail as follows.Generally, at least one of 10 access classes (for example, AC0, AC1, . .. , and AC9) may be randomly allocated to the UE. Exceptionally, forurgent emergency access, AC10 is allocated. As such, the value of therandomly allocated access class may be stored in each USIM of the UE1and the UE2. Then, the UE1 and the UE2 may verify whether the accessbarring is applied, by using a barring factor included in the receivedACB-related information, based on the stored access class. The accessbarring check may be performed in each access stratum (AS) layer, thatis, an RRC layer of the UE1 and the UE2.

The access barring check will be described in more detail as follows.

The ac-BarringPerPLMN-List may be included in the SIB type 2 received byeach of the UE1 and the UE2, and in the case where AC-BarringPerPLMNentry matched with plmn-identityIndex corresponding to the PLMN selectedin an higher layer is included in the ac-BarringPerPLMN-List,AC-BarringPerPLMN entry matched with the plmn-identityIndexcorresponding to the PLMN selected by the higher layer is selected.

Next, when the UE1 and the UE2 perform the RRC connection request, theaccess barring check may be performed by using T303 as Tharring andusing ac-BarringForMO-Data as a barring parameter.

When the barring is determined, each AS(RRC) layer of the UE1 and theUE2 may notify a failure of the RRC connection establishment to thehigher layer.

Subsequently, as such, when the access is barred, each AS(RRC) layer maydetermine whether a T302 timer or a Tbarring timer is running. If thetimer is not running, the T302 timer or the Tbarring timer may be run.

Meanwhile, while the T302 timer or a Tbarring timer is running, theAS(RRC) layer considers that all the access to the corresponding cell isbarred.

As described above, in the network overload and congest situation, thebase station may provide the ACB-related information to the UE. Then,the UE may check whether access to the cell is barred by using thebarring factor included in the received ACB information based on itsaccess class stored in the USIM. Through the access barring check,finally, an access attempt is not performed. That is, when the access tothe corresponding cell is barred through the access barring check, theUE does not attempt the access, and when the access to the correspondingcell is not barred, the UE attempts the access. The access barring checkis performed in the AS layer. Herein, the access attempt means that theAS(RRC) layer of the UE transmits the RRC connection request message tothe base station.

Meanwhile, the access barring check may perform general mobileoriginating (MO) services of the UE, for example, originating call,originating data, originating IMS voice, and originating IMS video. Thatis, the ACB may be applied to access of all application programs (but,except for a response to an emergency service or paging).

As a method of differentiating a normal mobile originating (MO) service,for example, originating call, originating data, originating IMS voice,and originating IMS video, it is proposed application specificcongestion control for data communication (ACDC).

FIG. 7 shows an example of access barring check for Application specificCongestion control for Data Communication (ACDC).

Referring to FIG. 7, firstly, a base station may provide ACDC barringinformation to a UE through SIB.

Meanwhile, when a specific application is executed in a UE and a datacommunication service is required by the specific application, anapplication layer for controlling execution of the specific applicationmay provide application attribute related information to an NAS layer.

Then, on the basis of the application attribute related informationreceived from the application layer, the NAS layer of the UE maydetermine an application category for the ACDC.

Subsequently, when starting a service request procedure for a serviceconnection (transmission of a service request message or transmission ofan extended service request message), the NAS layer of the UE maydeliver information regarding the application category to an AS layer(i.e., RRC layer).

Before performing the service request procedure of the NAS layer(transmission of the service request message or transmission of anextended service request message), on the basis of the applicationcategory and ACDC barring information received from the network, the ASlayer (e.g., RRC layer) of the UE may perform ACDC barring check andthus determines whether to allow or not allow the service requestprocedure.

If it is determined not to be barred but to be allowed as a result ofthe ACDC barring check, the AS layer (i.e., RRC layer) of the UE maytransmit an RRC connection request message to the base station.

As described above, a service request required by an applicationcurrently being executed in the UE through the ACDC may be allowed orbarred through differentiation.

Meanwhile, NG-RAN may support overload and access control functionalitysuch as RACH back off, RRC Connection Reject, RRC Connection Release andUE based access barring mechanisms. One unified access control frameworkmay be applied for NR. For each identified access attempt one AccessCategory and one or more Access Identities may be selected. NG-RAN maybroadcast barring control information associated with Access Categoriesand Access Identities and the UE may determine whether an identifiedaccess attempt is authorized or not, based on the broadcasted barringinformation and the selected Access Category and Access Identities. Inthe case of multiple core networks sharing the same NG-RAN, the NG-RANprovides broadcasted barring control information for each PLMNindividually. The unified access control framework may be applicable toall UE states. The UE states may include RRC_IDLE, RRC_INACTIVE orRRC_CONNECTED state. In RRC_IDLE, the UE NAS informs RRC of the accesscategory and the Connection Request includes some information to enablethe gNB to decide whether to reject the request.

Based on operator's policy, the 5G system shall be able to prevent UEsfrom accessing the network using relevant barring parameters that varydepending on Access Identity and Access Category. Access Identities areconfigured at the UE as listed in Table 2. Any number of these AccessIdentities may be barred at any one time.

TABLE 2 Access Identity number UE configuration 0 UE is not configuredwith any parameters from this table  1 (NOTE 1) UE is configured forMultimedia Priority Service (MPS).  2 (NOTE 2) UE is configured forMission Critical Service (MCS). 3-10 Reserved for future use 11 (NOTE 3)Access Class 11 is configured in the UE. 12 (NOTE 3) Access Class 12 isconfigured in the UE. 13 (NOTE 3) Access Class 13 is configured in theUE. 14 (NOTE 3) Access Class 14 is configured in the UE. 15 (NOTE 3)Access Class 15 is configured in the UE. (NOTE 1) Access Identity 1 isused by UEs configured for MPS, in the PLMNs where the configuration isvalid. The PLMNs where the configuration is valid are HPLMN, PLMNsequivalent to HPLMN, visited PLMNs of the home country, and configuredvisited PLMNs outside the home country. (NOTE 2) Access Identity 2 isused by UEs configured for MCS, in the PLMNs where the configuration isvalid. The PLMNs where the configuration is valid are HPLMN or PLMNsequivalent to HPLMN. (NOTE 3) Access Identities 11 and 15 are valid inHome PLMN only if the EHPLMN list is not present or in any EHPLMN.Access Identities 12, 13 and 14 are valid in Home PLMN and visited PLMNsof home country only. For this purpose the home country is defined asthe country of the MCC part of the IMSI.

Access Categories are defined by the combination of conditions relatedto UE and the type of access attempt as listed in Table 3. AccessCategory 0 shall not be barred, irrespective of Access Identities. Thenetwork can control the amount of access attempts relating to AccessCategory 0 by controlling whether to send paging or not.

TABLE 3 Access Category Type of number Conditions related to UE accessattempt 0 All MO signalling resulting from paging    1 (NOTE 1) UE isconfigured for delay All except for tolerant service and subject toEmergency access control for Access Category 1, which is judged based onrelation of UE's HPLMN and the selected PLMN. 2 All Emergency 3 Allexcept for the conditions in MO signalling Access Category 1. resultingfrom other than paging 4 All except for the conditions in MMTEL voiceAccess Category 1. (NOTE 3) 5 All except for the conditions in MMTELvideo Access Category 1. 6 All except for the conditions in SMS AccessCategory 1. 7 All except for the conditions in MO data that do notAccess Category 1. belong to any other Access Categories (NOTE 4) 8-31Reserved standardized Access Categories 32-63 (NOTE 2) All Based onoperator classification (NOTE 1) The barring parameter for AccessCategory 1 is accompanied with information that define whether AccessCategory applies to UEs within one of the following categories: a) UEsthat are configured for delay tolerant service; b) UEs that areconfigured for delay tolerant service and are neither in their HPLMN norin a PLMN that is equivalent to it; c) UEs that are configured for delaytolerant service and are neither in the PLMN listed as most preferredPLMN of the country where the UE is roaming in the operator-defined PLMNselector list on the SIM/USIM, nor in their HPLMN nor in a PLMN that isequivalent to their HPLMN. (NOTE 2) When there are an Access Categorybased on operator classification and a standardized Access Category toboth of which an access attempt can be categorized, and the standardizedAccess Category is neither 0 nor 2, the UE applies the Access Categorybased on operator classification. When there are an Access Categorybased on operator classification and a standardized Access Category toboth of which an access attempt can be categorized, and the standardizedAccess Category is 0 or 2, the UE applies the standardized AccessCategory. (NOTE 3) Includes Real-Time Text (RTT). (NOTE 4) Includes IMSMessaging.

One or more Access Identities and only one Access Category are selectedand tested for an access attempt. The 5G network shall be able tobroadcast barring control information (i.e. a list of barring parametersassociated with an Access Identity and an Access Category) in one ormore areas of the RAN. The UE shall be able to determine whether or nota particular new access attempt is allowed based on barring parametersthat the UE receives from the broadcast barring control information andthe configuration in the UE. In the case of multiple core networkssharing the same RAN, the RAN shall be able to apply access control forthe different core networks individually. The unified access controlframework shall be applicable both to UEs accessing the 5G CN usingE-UTRA and to UEs accessing the 5G CN using NR.

As described above, new 5G NR access category will be applied for accesscontrol. As new 5G NR access category will be applied, 4G LTE accesscontrol mechanisms cannot be applied for NR without any modification.When the UE is connected to 5G-CN via E-UTRA, the NAS layers of the UEand the AMF that the UE is connected to will exchange NR NAS signalingmessages. The serving eNB connected to 5G-CN may need to supportenhanced LTE signaling messages or support only LTE messages. The lattermay be preferred in order to minimize the modification impact of the eNBserving 5G-CN in that the RRC layers of the UE and the eNB can exchangelegacy LTE RRC messages. Here, the issue in the UE is that the NAS layeroperation is based on NR protocol and the RRC layer operation is basedon LTE protocol. The RRC layer in 4G LTE may require parameters such asestablishment cause, call type, EAB indication, or ACDC category fromthe NAS layer for access control. Therefore, the UE connected to 5G-NASvia E-UTRA may require functionality for compatible operation totranslate an access category into one or more LTE access controlparameters.

In the opposite case, the same problem may occur. When the UE isconnected to 4G-CN via serving gNB, the NAS layers of the UE and the MMEthat the UE is connected to will exchange LTE NAS signaling messages.Here, the issue in the UE is that the NAS layer operation is based onLTE protocol and the RRC layer operation is based on NR protocol. TheRRC layer in 5G may require access categories from the NAS layer foraccess control. Therefore, the UE connected to 4G-NAS via serving gNBmay require functionality for compatible operation to translate one ormore LTE access control parameters into one or more access categories.That is, for both NR and eLTE, the mapping between accesscategories/access identities and establishment cause value may beneeded.

Hereinafter, a method for a UE to perform access to a cell and anapparatus supporting the same according to an embodiment of the presentinvention are described in detail. According to an embodiment of thepresent invention, the UE may access the 5G-CN using E-UTRA. Forexample, the 5G-CN may include AMF, and the E-UTRA may include eNB.Alternatively, according to an embodiment of the present invention, theUE may access the 4G-CN using NR node. For example, the 4G-CN mayinclude MME, and the NR node may include gNB.

The UE connected to 5G-CN may exchange 5G NAS signalling messages withthe AMF no matter the serving node is the eNB or the gNB. Similarly, theUE connected to 4G-CN may exchange 4G NAS signalling messages with theMME no matter the serving node is the eNB or the gNB. According to anembodiment of the present invention, if the serving node is the eNB, theeNB and the UE may exchange LTE RRC messages for access control. On theother hand, if the serving node is the gNB, the gNB and the UE mayexchange NR RRC messages for access control. In this way, themodification impact in the UE and eNB serving 5G-CN or gNB serving 4G-CNcan be minimized. The UE RRC only concerns the connected serving node(e.g., whether the connected serving node is eNB using LTE signalling orgNB using NR signalling) and the UE NAS layer only concerns the RATinformation of the core network (e.g., whether the core network is 4G-CNor 5G-CN). Thus, no modification between the UE and the eNB may berequired to support access control, and no modification may be requiredfor the eNB connected to 5G-CN. To support this, the UE may maintain amapping table for parameter conversion from NR access control parametersinto LTE access control parameters to support LTE access controlmechanisms. For example, the LTE access control mechanisms includes atleast one of ACB, Extended Access Barring (EAB), Service Specific AccessControl (SSAC) or ACDC. Similarly, no modification between the UE andthe gNB may be required to support access control, and no modificationmay be required for the gNB connected to 4G-CN. To support this, the UEmay maintain a mapping table for parameter conversion from LTE accesscontrol parameters into NR access control parameters to support NRaccess control mechanisms. For example, the NR access control mechanismsincludes the access categories.

FIG. 8 is a block diagram illustrating access control mechanism for a UEconnected to 5G-CN via E-UTRA according to an embodiment of the presentinvention.

Referring to FIG. 8, the UE may maintain a mapping table for parameterconversion from NR access control parameters into LTE access controlparameters to support LTE access control mechanisms. The mapping tableis maintained in a NAS layer of the UE.

In first step, the UE may camp on a cell of a first system (or a firstRAT). The UE may receive barring information from the first system. Thefirst system (or the first RAT) may be LTE system. The barringinformation may include at least one of barring factor, barring time orbitmap.

In second step, if access to the cell is initiated for an NR accesscategory for the LTE system, the UE may convert the NR access categoryinto one or more LTE access control parameters based on the mappingtable. The LTE access control parameters may include at least one ofestablishment cause, call type, EAB indication or ACDC categories. TheNR access categories may be defined by the combination of conditionsrelated to the UE and the type of access attempt as listed in Table 3.For example, the UE may map one or more NR access categories to one ormore LTE access control parameters by using the mapping table. Forexample, the mapping table may be received from the LTE system or the NRsystem, and then the mapping table may be stored by the UE. For example,the mapping table may be pre-configured by the UE.

In third step, the UE may determine whether or not access to the cell isbarred by using the one or more LTE access control parameters and thebarring information. The one or more LTE access control parameters maybe converted, mapped or generated from the one or more NR accesscategories, based on the mapping table.

Alternatively, if the UE camps on a cell of a second system (or a secondRAT), and if access to the cell is initiated for the NR access categoryfor the second system (or the second RAT), the UE does not convert theNR access category into one or more LTE access control parameters basedon the mapping table. The second system (or the second RAT) may be NRsystem. Thus, the UE may determine whether or not access to the cell isbarred by using one or more NR access categories and the barringinformation, without using the mapping table.

In fourth step, if access to the cell is not barred, the UE may requestthe access to the cell.

For example, the following LTE access control mechanisms shall besupported when the UE is connected to 5G-CN via E-UTRA.

According to an embodiment of the present invention, the UE may performAccess Class Barring (ACB) based on barring information received inSIB2. The UE RRC layer may check if the access is allowed for a cell,when the UE performs RRC connection establishment. For this, the UE NASlayer shall provide call type (i.e. MO signalling, emergency call) forthe UE RRC layer maps it into RRC establishment cause. The parameter(s)provided by NAS may be converted to call type and establishment cause tosupport ACB. The parameter(s) provided by NAS may be one or more NRaccess categories.

According to an embodiment of the present invention, the networkoperator may perform EAB to UEs configured for EAB for network overloadcontrol such that the network can restrict access the UEs whencongestion occurs. The parameter(s) provided by NAS may be converted toEAB indication to support EAB. The parameter(s) provided by NAS may beone or more NR access categories.

According to an embodiment of the present invention, ACDC may preventaccess attempts from a particular application. The parameter(s) providedby NAS may be converted to ACDC category to support ACDC. Theparameter(s) provided by NAS may be one or more NR access categories.

According to an embodiment of the present invention, the UE configuredfor NAS signalling low priority may indicate it when the UE performs RRCconnection establishment or RRC resume. When the network rejects therequest, the network may send timer so that the UE cannot attempt accessfor a given time. The parameter(s) provided by NAS may be converted tocall type to support delay tolerant access. The parameter(s) provided byNAS may be one or more NR access categories.

According to an embodiment of the present invention, E-UTRAN may supportSSAC for IMS telephony services (i.e., MMTEL). If the UE determines thebarring status in the IMS engine and the IMS engine supports SSAC for5G, SSAC shall be supported regardless of the serving node. If IMSengine supports legacy SSAC operation for 5G, SSAC will be supportedwithout any impact on RRC.

Since the NAS layer will provide NR access category information to theRRC layer in NR and most LTE access control mechanisms are performedbased on NAS information, the NAS layer may maintain the mapping table.

FIG. 9 is a block diagram illustrating access control mechanism for a UEconnected to 4G-CN via NR Radio Access (NR) according to an embodimentof the present invention.

Referring to FIG. 9, the UE may maintain a mapping table for parameterconversion from LTE access control parameters into NR access controlparameters to support NR access control mechanisms. The mapping table ismaintained in a NAS layer of the UE.

In first step, the UE may camp on a cell of a second system (or a secondRAT). The UE may receive barring information from the second system. Thesecond system (or the second RAT) may be NR system. The barringinformation may include at least one of barring factor, barring time orbitmap.

In second step, if access to the cell is initiated for an LTE accesscontrol parameter for the NR system, the UE may convert the LTE accesscontrol parameter into one or more NR access categories based on themapping table. The LTE access control parameters may include at leastone of establishment cause, call type, EAB indication or ACDCcategories. The NR access categories may be defined by the combinationof conditions related to the UE and the type of access attempt as listedin Table 3. For example, the UE may map one or more LTE access controlparameters to one or more NR access categories by using the mappingtable. For example, the mapping table may be received from the LTEsystem or the NR system, and then the mapping table may be stored by theUE. For example, the mapping table may be pre-configured by the UE.

In third step, the UE may determine whether or not access to the cell isbarred by using the one or more NR access categories and the barringinformation. The one or more NR access categories may be converted,mapped or generated from the one or more LTE access control parameters,based on the mapping table.

Alternatively, if the UE camps on a cell of a first system (or a firstRAT), and if access to the cell is initiated for the LTE access controlparameter for the first system (or the first RAT), the UE does notconvert the LTE access control parameter into one or more NR accesscategories based on the mapping table. The first system (or the firstRAT) may be LTE system. Thus, the UE may determine whether or not accessto the cell is barred by using one or more LTE access control parametersand the barring information, without using the mapping table.

In fourth step, if access to the cell is not barred, the UE may requestthe access to the cell.

FIG. 10 is a flow chart illustrating access control mechanism of a UEaccording to an embodiment of the present invention.

Referring to FIG. 10, in step S1000, the UE may retrieves a mappingtable from a Subscriber identification module (SIM) card or non-volatilememory. The mapping table may be pre-configured by the UE. The mappingtable may be configured from the network. For example, the network mayinclude NR system and LTE system. The mapping table is for converting ormapping 5G NR parameters into 4G LTE parameters. The mapping table isfor converting or mapping 4G LTE parameters into 5G NR parameters. Evenif the mapping table is pre-configured by the UE, the UE can receive themapping table from the network. In this case, if there existspre-configured mapping table in step S1000 and same parameters exist,the values received from the network has priority. For example, the UEmay be configured as a machine type communication (MTC) device.

In step S1010, the UE may apply MIB, SIBs and SI messages. The RRC layerof the UE may store information for access control as well as otherfunctionalities.

In step S1020, the UE may trigger mobile originated signalling.

In step S1030, the UE may determine whether or not to perform parameterconversion (or parameter mapping).

If the UE determines to perform parameter conversion (or parametermapping), in step S1040, the UE converts or maps between 4G LTEparameters and 5G NR parameters using the mapping table. For NAStriggered events, UE NAS may perform the mapping to AS cause value whenUE NAS makes a request to UE AS for access. Further, the UE NAS may alsoprovide cause value for AS triggered events. At least one LTEestablishment cause value, such as emergency, highPriorityAccess,mt-Access, mo-Signalling, mo-Data, or mo-VoiceCall-v1280, may be reusedfor NR.

If the UE determines not to perform parameter conversion (or parametermapping), the UE does not convert or map between 4G LTE parameters and5G NR parameters.

For example, in case of the UE connecting to 5G-CN via E-UTRA, the UEmay convert or map NR access control parameter ‘access category=2’ intoLTE parameters ‘establishment cause=MO signalling, call type=originatingsignalling’ using the mapping table. Then, if the UE is allowed toattempt access, the UE may send a RRC connection establishment requestmessage indicating ‘establishment cause=MO signalling’.

For example, in case of the UE connecting to 5G-CN via E-UTRA, the UEmay convert or map NR access control parameter ‘access category=4,access category=6’ into LTE parameters ‘establishment cause=Delaytolerant, call type=originating signalling’ using the mapping table.Then, if the UE is allowed to attempt access, the UE may request a RRCconnection establishment message indicating ‘establishment cause=Delaytolerant’. If the request of the UE is rejected with extendedWaitTime,the RRC layer of the UE may forward the extendedWaitTime to the NASlayer of the UE, and also inform about the failure.

For example, in case of the UE connecting to 4G-CN via NG-RAN, the UEmay convert or map LTE parameters ‘establishment cause=MO signalling,call type=originating signalling’ into NR access control parameter‘access category=2’ using the mapping table. Then, if the UE is allowedto attempt access, the UE may send a RRC connection establishmentrequest message indicating ‘access category=2’.

For example, in case of the UE connecting to 4G-CN via NG-RAN, the UEmay convert or map LTE parameters ‘establishment cause=Delay tolerant,call type=originating signalling’ into NR access control parameter‘access category=4, access category=6’ using the mapping table. Then, ifthe UE is allowed to attempt access, the UE may request a RRC connectionestablishment message indicating ‘access category=4, access category=6’.If the request of the UE is rejected with extendedWaitTime, the RRClayer of the UE may forward the extendedWaitTime to the NAS layer of theUE, and also inform about the failure.

For example, in case of the UE connecting to 5G-CN via E-UTRA, it isassumed that the UE performs inter-RAT handover and connects to 4G-CNvia E-UTRA. If the UE triggers mobile originated signalling, the UEneeds not refer the mapping table, because NAS layer will provide LTEparameters. Then, the UE checks access barring and requests RRCconnection establishment message if allowed.

FIG. 11 is a block diagram illustrating a method for a UE to performaccess to a cell according to an embodiment of the present invention.

Referring to FIG. 11, in step S1110, the UE may receive, from a firstsystem, access control information for the first system. The accesscontrol information for the first system may be provided by a non-accessstratum (NAS) layer of the UE. The UE may connect with a core network ofthe first system, via a base station of the second system.

In step S1120, the UE may camp on the cell of a second system.

In step S1130, the UE may map the access control information for thefirst system to access control information for the second system. Theaccess control information for the first system may include at least oneNR access category. The access control information for the second systemmay include at least one of establishment cause, call type, extendedaccess barring (EAB) indicator or Application specific Congestioncontrol for Data Communication (ACDC) categories.

Additionally, the UE may configure a mapping table for mapping theaccess control information for the first system to the access controlinformation for the second system. The access control information forthe first system may be mapped, by a non-access stratum (NAS) layer ofthe UE, to the access control information for the second system, basedon the configured mapping table. The mapping table may be pre-configuredby the UE. The mapping table may be received from the first system orthe second system. The mapping table received from the first system orthe second system may have higher priority than the mapping tablepre-configured by the UE.

Additionally, the UE may receive, from the second system, barringinformation including at least one of barring factor, barring time orbitmap.

In step S1140, the UE may perform access to the cell of the secondsystem, based on the mapped access control information for the secondsystem. The access to the cell of the second system may be performedbased on the mapped access control information for the second system, ifthe access to the cell of the second system is not barred.

The first system may be NR radio access (NR) system, and the secondsystem may be long-term evolution (LTE) system. Alternatively, the firstsystem may be long-term evolution (LTE) system, and the second systemmay be NR radio access (NR) system.

According to an embodiment of the present invention, the UE may mapbetween one or more NR access categories and one or more LTE accesscontrol parameters by using the mapping table. Thus, in case of the UEconnecting to 5G-CN via E-UTRA or the UE connecting to 4G-CN via NG-RAN,the UE can perform access control without signaling modification amongthe UE, the base station and the core network.

FIG. 12 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

A BS 1200 includes a processor 1201, a memory 1202 and a transceiver1203. The memory 1202 is connected to the processor 1201, and storesvarious information for driving the processor 1201. The transceiver 1203is connected to the processor 1201, and transmits and/or receives radiosignals. The processor 1201 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the basestation may be implemented by the processor 1201.

A UE 1210 includes a processor 1211, a memory 1212 and a transceiver1213. The memory 1212 is connected to the processor 1211, and storesvarious information for driving the processor 1211. The transceiver 1213is connected to the processor 1211, and transmits and/or receives radiosignals. The processor 1211 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the basestation may be implemented by the processor 1211.

The processor may include an application-specific integrated circuit(ASIC), a separate chipset, a logic circuit, and/or a data processingunit. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother equivalent storage devices. The transceiver may include abase-band circuit for processing a wireless signal. When the embodimentis implemented in software, the aforementioned methods can beimplemented with a module (i.e., process, function, etc.) for performingthe aforementioned functions. The module may be stored in the memory andmay be performed by the processor. The memory may be located inside oroutside the processor, and may be coupled to the processor by usingvarious well-known means.

Various methods based on the present specification have been describedby referring to drawings and reference numerals given in the drawings onthe basis of the aforementioned examples. Although each method describesmultiple steps or blocks in a specific order for convenience ofexplanation, the invention disclosed in the claims is not limited to theorder of the steps or blocks, and each step or block can be implementedin a different order, or can be performed simultaneously with othersteps or blocks. In addition, those ordinarily skilled in the art canknow that the invention is not limited to each of the steps or blocks,and at least one different step can be added or deleted withoutdeparting from the scope and spirit of the invention.

The aforementioned embodiment includes various examples. It should benoted that those ordinarily skilled in the art know that all possiblecombinations of examples cannot be explained, and also know that variouscombinations can be derived from the technique of the presentspecification. Therefore, the protection scope of the invention shouldbe determined by combining various examples described in the detailedexplanation, without departing from the scope of the following claims.

What is claimed is:
 1. A method of performing, by a user equipment (UE),an access attempt to a cell in a wireless communication system, themethod comprising: triggering the access attempt to the cell;determining an access category related to the access attempt; mappingthe access category to an establishment cause based on a mapping table;and based on the access attempt not being barred, transmitting, to abase station of the cell, a message requesting establishment of a radioresource control (RRC) connection, the message comprising theestablishment cause mapped from the access category.
 2. The method ofclaim 1, wherein the UE is connected to a core network of a NR system.3. The method of claim 1, further comprising: performing the accessattempt to the cell.
 4. The method of claim 3, wherein the accessattempt to the cell is performed based on the establishment cause. 5.The method of claim 3, wherein the access attempt to the cell isperformed based on the access category.
 6. The method of claim 1,wherein the access category is related to NR system, and theestablishment cause is related to LTE system.
 7. The method of claim 1,wherein the establishment cause is transmitted to the BS, when theaccess attempt to the cell is allowed for the UE.
 8. The method of claim1, further comprising: configuring the mapping table for mapping theaccess category to the establishment cause.
 9. The method of claim 8,wherein the access category is mapped, by a non-access stratum (NAS)layer of the UE, to the establishment cause based on the mapping table.10. The method of claim 8, wherein the mapping table is pre-configuredby the UE.
 11. The method of claim 1, wherein the access category isprovided, by a non-access stratum (NAS) layer of the UE, to a radioresource control (RRC) layer of the UE.
 12. The method of claim 1,wherein the establishment cause mapped from the access category isprovided, by a non-access stratum (NAS) layer of the UE, to a radioresource control (RRC) layer of the UE.
 13. The method of claim 1,further comprising: receiving, from the base station, barringinformation including at least one of barring factor, barring time orbitmap.
 14. The method of claim 1, wherein the access category is aninteger value.
 15. The method of claim 1, wherein the access category isdetermined by a non-access stratum (NAS) layer of the UE.
 16. The methodof claim 1, wherein the access category is determined by a radioresource control (RRC) layer of the UE.
 17. A user equipment (UE)configured to perform an access attempt to a cell in a wirelesscommunication system, the UE comprising: a transceiver; at least oneprocessor; and at least one computer memory operably connectable to theat least one processor and storing instructions that, when executed,cause the at least one processor to perform operations comprising:triggering the access attempt to the cell; determining an accesscategory related to the access attempt; mapping the access category toan establishment cause based on a mapping table; and based on the accessattempt not being barred, transmitting, to a base station of the cell, amessage requesting establishment of a radio resource control (RRC)connection, the message comprising the establishment cause mapped fromthe access category.
 18. The UE of claim 17, wherein the UE is connectedto a core network of a NR system.
 19. The UE of claim 17, wherein theaccess attempt to the cell is performed based on the access category.20. The UE of claim 17, wherein the mapping table for mapping the accesscategory to the establishment cause is configured for the UE.